A recent trend toward a small, thin mobile device leads to a strong demand for a small, thin piezoelectric device used in the device.
FIG. 17 is a diagram showing a piezoelectric device in the prior art. As shown in FIG. 17A, a piezoelectric device 50 in the prior art comprises a package 53 that has a cavity 52 for storing a piezoelectric vibration element 51 and a mounting stand 58 that has an electrode 57 connected electrically to an external connection terminal 56; the piezoelectric vibration element 51 one end of which is supported and fixed on the electrode 57, formed on the mounting stand 58, using a conductive adhesive 55; and a lid 54 for hermetically sealing the package 53.
In the case of the piezoelectric device 50 shown in FIG. 17A, the electrode 57 that functions as the mounting portion for supporting and fixing the piezoelectric vibration element 51 is provided in a position away from the center of gravity of the piezoelectric vibration element 51. Because the conductive adhesive 55 used generally for fixing the piezoelectric vibration element 51 is liquid in many cases, the unsupported, unfixed end of the piezoelectric vibration element 51 easily hangs down due to the weight of the piezoelectric vibration element 51 itself, as shown in FIG. 17B, after applying the conductive adhesive 55 to the electrode 57 and then mounting the piezoelectric vibration element 51 in a predetermined position but before heat-hardening the adhesive.
The unsupported, unfixed end of the piezoelectric vibration element 51, which hangs down as shown in FIG. 17B, comes into contact with the bottom face of the cavity 52 of the package 53, causing deterioration in the characteristics of the piezoelectric device 50. To solve this problem, the structure is employed in which the mounting stand 58 is formed in the package 53 to provide space between the bottom face of the cavity 52 and the piezoelectric vibration element 51 so that the end of the piezoelectric vibration element 51 does not come into contact with the bottom face of the cavity 52 even when it hangs down. However, the problem with this structure is that the mounting stand 58, if provided, prevents the piezoelectric device 50 from becoming thinner.
Therefore, to provide a thin piezoelectric device, the configuration is proposed in which the central leg is provided between two vibration legs and this central leg supports the piezoelectric device. For example, Patent Document 1 discloses a piezoelectric device having the configuration in which the piezoelectric device is supported at one point that is the center of gravity of the central leg provided between two vibration legs, and Patent Document 2 discloses a piezoelectric device having the configuration in which the piezoelectric device is supported at two points on the central leg.
FIG. 18 is a diagram showing the structure of a piezoelectric device in another prior art described in Patent Document 2.
FIG. 18 is a top view showing the piezoelectric device in the prior art. As shown in FIG. 18, a piezoelectric vibration element 61 in the prior art has a central leg 61b between two vibration legs 61a, and electrodes 64 provided on this central leg 61b are electrically and mechanically supported and fixed on two conductive pads 66, electrically connected to external connection terminals (not shown), using conductive adhesive 65. In the package, the piezoelectric vibration element 61 is supported and fixed in the same positions where the electrodes 64 are formed.
This configuration prevents the leading end of the piezoelectric vibration element from hanging down and coming into contact with the bottom face of the cavity, as shown in the example in the prior art shown in FIG. 17, when the piezoelectric vibration element is installed in the package.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-163568    Patent Document 2: Japanese Patent Laid-Open Publication No. 2006-345519